TY - JOUR
T1 - The chloroplast trnT-trnF region in the seed plant lineage Gnetales
AU - Won, Hyosig
AU - Renner, Susanne S.
PY - 2005/10
Y1 - 2005/10
N2 - The trnT-trnF region is located in the large single-copy region of the chloroplast genome. It consists of the trnL intron, a group I intron, and the trnT-trnL and trnL-trnF intergenic spacers. We analyzed the evolution of the region in the three genera of the gymnosperm lineage Gnetales (Gnetum, Welwitschia, and Ephedra), with especially dense sampling in Gnetum for which we sequenced 41 accessions, representing most of the 25-35 species. The trnL intron has a conserved secondary structure and contains elements that are homologous across land plants, while the spacers are so variable in length and composition that homology cannot be found even among the three genera. Palindromic sequences that form hairpin structures were detected in the trnL-trnF spacer, but neither spacer contained promoter elements for the tRNA genes. The absence of promoters, presence of hairpin structures in the trnL-trnF spacer, and high sequence variation in both spacers together suggest that trnT and trnF are independently transcribed. Our model for the expression and processing of the genes tRNAThr(UGU), tRNALeu(UAA), and tRNAPhe (GAA) therefore attributes the seemingly neutral evolution of the two spacers to their escape from functional constraints.
AB - The trnT-trnF region is located in the large single-copy region of the chloroplast genome. It consists of the trnL intron, a group I intron, and the trnT-trnL and trnL-trnF intergenic spacers. We analyzed the evolution of the region in the three genera of the gymnosperm lineage Gnetales (Gnetum, Welwitschia, and Ephedra), with especially dense sampling in Gnetum for which we sequenced 41 accessions, representing most of the 25-35 species. The trnL intron has a conserved secondary structure and contains elements that are homologous across land plants, while the spacers are so variable in length and composition that homology cannot be found even among the three genera. Palindromic sequences that form hairpin structures were detected in the trnL-trnF spacer, but neither spacer contained promoter elements for the tRNA genes. The absence of promoters, presence of hairpin structures in the trnL-trnF spacer, and high sequence variation in both spacers together suggest that trnT and trnF are independently transcribed. Our model for the expression and processing of the genes tRNAThr(UGU), tRNALeu(UAA), and tRNAPhe (GAA) therefore attributes the seemingly neutral evolution of the two spacers to their escape from functional constraints.
KW - Gnetales
KW - Gymnosperms
KW - Palindromic sequences
KW - trnL intron
KW - trnL-trnF intergenic spacer
KW - trnT-trnL intergenic spacer
UR - http://www.scopus.com/inward/record.url?scp=26244463341&partnerID=8YFLogxK
U2 - 10.1007/s00239-004-0240-3
DO - 10.1007/s00239-004-0240-3
M3 - Article
C2 - 16155750
AN - SCOPUS:26244463341
SN - 0022-2844
VL - 61
SP - 425
EP - 436
JO - Journal of Molecular Evolution
JF - Journal of Molecular Evolution
IS - 4
ER -